Video editing/face replace
Open the "Motion Tracking" layout.
Load your video





Track high contrast points (ctrl+LMB to create a tracking point, then press the track forward/backward buttons)





Change the layout to "Video Editing"
Drag in your tracked footage
Drag in your image file
Use the VSE_Transform_Tools addon to position and size your image over the face


Alt+S will rescale an image to it's original aspect ratio FYI

Use the "Transform from 2D Track" function (also part of the VSE_Transform_Tools addon) to pin the image to the face.